Users can interact with many database systems by submitting Structured Query Language (SQL) statements to the database systems. SQL is a non-procedural language enabling users to describe a desired operation using reserved SQL commands. The database server then generates procedures based on the SQL commands to perform the desired operation.
One disadvantage of an SQL-based database system is that a user is generally limited to the operations supported by the standard sets of SQL commands. To provide increased flexibility, some database vendors have developed extensions to the SQL language. For example, the PL/SQL language developed by the Oracle Corporation provides a procedural language extension to SQL commands. Although users may invoke defined functions created using standard SQL or PL/SQL commands, conventional database systems do not enable users to invoke external routines, such as routines created using a third generation languages such as "C" or "C++".
Some database systems have attempted to enhance database capabilities by linking external routines directly to server processes, where the linked external routines are executed within the same address space as the server process. This arrangement suffers the disadvantage that the linking of the external routines inherently creates potential operating risks to the database system. For example, if a C program linked to the database server had an execution error, then the error during execution of the C program may result in crashing of the entire database system.
Some database systems have attempted to limit the harmful effects of linked external routines by preventing the external routines from accessing address space that is reserved for critical database server processes. In such cases, however, failures in the linked external routines may still adversely affect the server processes since the server process would need to carefully manage internal operations in order to keep the crash of the external routine from expanding into the database server. Thus, the prior art systems cannot guarantee that a database server will not crash during execution of a linked external procedure.